The present invention relates to a substrate transport apparatus and a heat treatment apparatus which place a substrate such as a semiconductor substrate, a glass substrate for a liquid crystal display device, a glass substrate for a photomask, a substrate for an optical disk and the like on a holding surface to perform a heat treatment on the substrate.
As is well known, semiconductor and liquid crystal display products and the like are fabricated by performing a series of processes including cleaning, resist coating, exposure, development, etching, interlayer insulation film formation, heat treatment, dicing, and the like on the above-mentioned substrate. An apparatus which performs a resist coating process on a substrate to transfer the substrate to an exposure unit and which receives an exposed substrate from the exposure unit to perform a development process on the exposed substrate, among the above-mentioned processes, is widely used as a so-called coater-and-developer.
The exposure unit (also known as a stepper) for performing an exposure process is typically provided in juxtaposition with the above-mentioned coater-and-developer, and prints a circuit pattern on a substrate formed with a resist film. With recent decrease in width of lines exposed to light, a lamp for use in printing of a pattern in such an exposure unit is shifting from a conventional ultraviolet light source toward a KrF excimer laser light source and also toward an ArF excimer laser light source. A chemically amplified resist is used when a pattern is printed using a KrF light source and an ArF light source. The chemically amplified resist is a photoresist of the type in which an acid formed by a photochemical reaction during the exposure process acts as a catalyst for resist reactions such as crosslinking, polymerization and the like in the subsequent heat treatment step to change the solubility of the resist in a developing solution, whereby pattern printing is completed.
It is known that, when the chemically amplified resist is used, a slight variation in processing conditions exerts a large influence upon line width uniformity because an extremely small amount of acid catalyst is formed during the exposure process. Thus, an attempt has been made to make various processing conditions throughout the exposure processing step as uniform as possible when the chemically amplified resist is used. A technique for controlling the time interval between the instant of the end of the exposure process and the instant of the start of a post-exposure bake process to be constant to make the line widths of a pattern uniform is proposed, for example, in Japanese Patent Application Laid-Open No. 2002-43208 and Japanese Patent Application Laid-Open No. 2004-342654.
However, slight line width nonuniformity has not yet been eliminated despite various improvements, and is generally considered to result principally from the post-exposure bake process. Like other heating processes, the post-exposure bake process includes the steps of increasing the temperature of a substrate, maintaining the substrate at a predetermined temperature, and then decreasing the temperature of the substrate. Of these steps, the step of increasing the temperature of the substrate and the step of maintaining the substrate at the predetermined temperature can attain in-plane uniformity of the substrate with considerably high accuracy. Despite accurate control over the in-plane uniformity of the substrate during this step, line width nonuniformity still exists. Thus, there is a need in the art for improved methods and systems for performing substrate processing operations including heat treatment operations.